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New York City Could See More Frequent Floods in the Future

3 Nov 2017, 2:06 pm

From Penn St. University

Rising sea levels threaten greater future storm damage to New York City, but the paths of stronger future storms may shift offshore, changing the coastal risk for the city, according to a team of climate scientists.

“If we cause large sea-level rise, that dominates future risks, but if we could prevent sea-level rise and just have the storm surge to worry about, our projections show little change in coastal risk from today during most years,” said Michael E. Mann, distinguished professor of meteorology and atmospheric science and director of Penn State’s Earth System Science Center. “While those storms that strike New York City might be bigger and stronger, there may be fewer of them as changing storm tracks increasingly steer the storms away from NYC and toward other regions.”

Coastal damage increases if the sea level is higher before a storm, and if the extra surge caused by the storm is higher.

[Street map of New York City showing maximum projected future storm surge.  Natural water is in dark blue, 2100 levels are in medium blue and 2300 levels are in light blue.]

The researchers looked at the history and future of both sea level and storm surge, from preindustrial times through 2300, in models that had been run for the full period. The researchers focused on results from simulations with rapid carbon dioxide release, often referred to as “business-as-usual” simulations. They reported their results in the Proceedings of the National Academy of Sciences.

The researchers first calibrated their sea-level models to simulate the rates of historic sea-level rise. Then they ran simulations for the future, with and without results of a recent study that projects large future Antarctic ice sheet melt with business-as-usual increases in levels of greenhouse gases. Such large Antarctic melt implies large increases in sea level, globally and at New York City.

If this Antarctic instability occurs, the future risk to New York City is dominated by sea level rise. Then, according to Andra J. Gardner, postdoctoral fellow, Rutgers University, by 2100 the estimated 500-year flood height would be 17 feet, and by 2300 the 500-year flood height would be about 50 feet. A 500-year flood is one that has a 1 in 500 chance of occurring in any given year.

[“New York District continues supporting New York and New Jersey Harbor after Hurricane Sandy” by USACE NY is licensed under CC BY 2.0]

If sea-level rise remains small, then changes in storm surge are the most important concern for future coastal risk to New York City. In agreement with previous work, the models show that warmer future conditions allow stronger storms. The models also show that the warming causes storm tracks to shift offshore and northward, away from New York City, and identifies important differences that could be reduced with further research.

“If a shift occurs toward less common but possibly larger storms, it poses special challenges for coastal planners, and highlights the value of additional progress in understanding and projecting the tracks as well as the strength of these storms,” said Mann.

“Sea level is rising and higher sea level increases the damages from coastal storms,” said Richard B. Alley, Evan Pugh Professor of Geosciences, Penn State. “Human decisions about energy will be important in determining how much the sea rises and thus how much damage we face, and accurate projections of storms will help in minimizing the risks.”

Edited for WeatherNation by Meteorologist Mace Michaels

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